importing photos from iPhone to LightRoom, I check Don't import suspected duplicates but it does

I posted this to an Adobe forum a couple days ago and got no responses so far.

Since this problem doesn't exist with two cameras but does with my iPhone 6S maybe it is an iPhone or iOS problem so I'm posting the same question here.

The title is the summary, but here are the gory details

Latest OS X on a MacBook Pro

Latest Creative Cloud (LightRoom)

iPhone 6S Plus with latest iOS

I got a new iPhone a week ago (went from 5S to 6S Plus).

Just before I got the new phone I did an import to LightRoom and a backup to iTunes of my old iPhone, which was also at the newest iOS.

I loaded my new iPhone with the backup from iTunes - lots of photos since 6 February went onto the new iPhone.

Yesterday I did a new import from my new iPhone to LR - everything worked smoothly. No duplicates were imported.

I took a bunch of iPhone photos today.

Now when I try to import it shows all the photos on the iPhone not grayed out and with the checkmark and with the directories on the right indicating the number of files that will be headed to each (I use YYYY/MM/DD folders for all my photos from three cameras) even though I check "Don't import suspected duplicates".

In the past I have searched for every file with *-2.JPG in its name and deleted them (in LR, not Finder) - but I'm tired of it.

Since I wrote the above the same thing has happened two more times - every time I import from my 6S+ to LightRoom it wants to bring all the photos in and create duplicates of the existing ones - but I do not see the same bad behavior with a Canon and an Olympus.

I'm doing a workshop with my camera club in a few weeks and I'd like to give them a heads up on this.